In recent years, light-emitting diodes (LEDs) have come into use as the light source of a lighting unit. Since a light-emitting diode has a longer life and generates less heat than an incandescent lamp and the like, a plurality of (two or more) light-emitting diodes coupled to each other can be used. As an example, there is proposed the idea of coupling a plurality of light-emitting diodes with a sheet-like conductor to form a strip-like light source coupler (LED module) (see, e.g., Patent Literature 1).